Existing fuel-dispensing nozzles include a certain number of safety systems to prevent fuel from being split on the ground. Mention may be made of mechanisms which interrupt fuel dispensing when a vehicle tank is full and mechanisms which prevent fuel from leaving the nozzle when its spout end is pointing upwards.
These various safety systems generally serve to decouple the actuating lever of the nozzle from a flow control valve which is normally controlled by the lever. Such decoupling is normally obtained by means of a detection channel received inside the spout of the nozzle and having its ends opening out respectively to the end of the spout and in a venturi tube formed between the valve member of the flow control valve and its seat. The flow of fuel through the valve creates suction in the venturi tube which in turn produces a vacuum inside the detection channel as soon as its other end is closed, i.e. when the vehicle tank is full and the fuel level in the vehicle tank rises up to the spout and thus closes the detection channel. A membrane responsive to the pressure inside the channel responds to the vacuum created in this way by moving and causing the mechanical connection between the lever and the valve member to be interrupted. Any action on the lever has no effect on the flow control valve so the flow of fuel is interrupted.
This safety system is generally accompanied by a second valve member located in the detection channel and operating under gravity. When the fuel-dispensing nozzle points upwards, this valve closes the channel automatically by gravity. This closure causes the lever to be decoupled from the valve member of the flow control valve in the same manner as before.
However, in practice, it turns out that these safety systems are sometimes insufficient for preventing an accidental flow of fuel outside a vehicle tank. In particular, it is always possible to obtain a flow of fuel by actuating the lever when the nozzle is pointing downwards and while not engaged in the filling tube of a vehicle tank. In this case, the fuel that is split onto the ground of the filling station causes a nuisance and may give rise to accidents.